Iiynamically compensated weighing scales

ABSTRACT

3. A WEIGHING SYSTEM COMPRISING A FIRST SCALE, FIRST TRANSDUCER MEANS FOR TRANSMITTING A SIGNAL PROPORTIONAL TO THE LOAD APPLIED TO SAID SCALE, A COMPENSATOR INCLUDNG A SUSPENSION COUPLED TO SAID SCALE, SECOND TRANSDUCER MEANS (FOR TRANSMITTING A SIGNAL PROPORTIONAL TO THE MOVEMENT OF SAID COMPENSATOR), RATE SENSITIVE MEANS FOR PRODUCING A SECOND SIGNAL PROPORTIONAL TO THE RATE OF MOVEMENT OF THE SCALE FOR CONNECTING SAID SCALE AND COMPENSATOR WHEREBY SAID SECOND TRANSDUCER MEANS PRODUCES SAID (A) SIGNAL PROPORTIONAL TO THE RATE OF MOVEMENT OF SAID SCALE AND MEANS CONNECTING SAID FIRST AND SECOND SIGNALS.

Jan. 14, 1975 Original F11 RESUL 74? DYNAIICALLY COHPEHSATED WEIGHINGSCALES 4 Sheets-Shut s. a. BLODGETT} ed June 15, 1962 I" CUT OFFIMATERIAL VALVE AND 1 SUPPLY} 1 ACTUATOR 1 CUMPEMSWZ'OE Jan. 14, 1975 s.a. 5 0 TT Re. 28,303

DYNAHICALLY COMPENSATED WBIGHING SCALES Original Filed June 1 1962 4Sheets-Sheet 2 Jan. 14, 1975 s. B. BLODGETT Re. 28,303

DYNAMICALLY GOHPENSATED WEIGHING SCALES Original Filed June 15, 1962 4Sheets-Sheet 4.

5 L u 70 1" 66 r:

United States Patent Oifice 28.303 DYNAMICALLY CgElAPIENSATED WElGllINGStewart B. Blndgett, Houston, Tex., asslgnor to Blodgett ManufacturingCompany, a division of Mira-Palt, Inc. Original No. 3.142.349. datedJuly 28, 1964, Ser. No.

202,884. June 15, 1962. Application for reissnte May 23, i973, Ser. No.363.146

Int. Cl. Gtllg 23/14 US. Cl. 171-164 26 Claims Matter enclosed in heavybrackets I 1 appears in the original patent but forms no part of thisreLssue specification: matter printed in italics indicates the additionsmade by reissue.

The present invention provides a method and apparatus for increasing theaccuracy of scales used for rapid repetitive weighing by compensatingfor effects of transient loading such as those derived from impact ofsolid articles being weighed or the vibration of the scale as a wholeor, alternatively, for the weight of material still entering theweighing pan when the desired weight is indicated. My invention providesa novel, useful weighing device wherein these compensations are attainedby coupling a compensating system to the weighing scale by meansresponsive to vibration and impact loading or responsive to the rate offeed of the material to the weighing scale and connecting the outputs ofthe compensating system and weighing scale to eflect compensation in theresultant scale reading.

in the packaging industry, the product is frequently weighed while it isbeing fed to the s:ale in order to control the weight of the finishedpackage. When conventional scales are used at practical filling spccdsthere are a number of factors which meet the accuracy of the packageweight. In certain applications where material is being fed to a scalepan the cu off valve is located a finite distance from the scale pan andhence there may be material in the air past the cut oli' valve when thevalve is closed at the time the cut oil weight is indicated on theweighing scale. Compensation must be made for the weight of thismaterial in the air to reduce variations in the weight of the packages.ll there is variation in material density or in the feed rate at whichmaterial is entering the scale, loss of accuracy may result. in adlli'erent utilization, the initial loading due to the impact of solidobjects being weighed on the scale pan may be the primary source oferror. For items such as hard candy or dog biscuits, this elfect may bemore important than the weight of the column of material in the air. instill another case, packages may be transported to the pan of the scalefrom a movable belt resting on the pan. For example, a belt might beused to transport and permit weighing of lilled packages for the purposeof rejecting packages falling outside of a certain weight tolerance orto cause corrective action to be taken at the filling ma chine. Whenconventional scales are used, accuracy may be aflected by beltvibration, belt flutter, or other irregularities. in larger scales, acomplete conveyor drive may be mounted on the scale platform. Here thevibration of the platform from the motor and drive mechanism, as well asvibration from the floor will all'ect accuracy. Whatever the manner ofloading the pan of the scale, all weighing instruments will suiier fromvibration of the scale mount as a whole due to floor movement or otherunavoidable vibrations of the building.

Obviously, vibration compensation could be achieved by providing twosimilar scales which will respond to vibration similarly and by [the]coupling the outputs of these scales so that they tend to subtract inorder to nullify the eliects of vibration. However, upon varying theweigh. on one scale, the response to vibration of that scale will Re.28,303 Reissued Jan. 14, 1975 be altered so that the output of the twoscales will not necessarily nullity the effects of vibration and may,ill tact, tend to increase such etl'ects, since the outputs of thescales are not in phase and the signals will not tend to cancel eachother. thus, such a system of vibration compcnsation is not effectivesince it achieves the desired obiectivc only at one specific scaleloading.

According to one embodiment of the invention first and second scalemeans are interconnected by a coupling which causes substantially equalresponse in the second or compensating scale means to movements of thescale pan of the first scale means of a higher velocity than thatexperienced by normal teed rates. Thus, both said first and second scalemeans respond substantially equally to vibrations regardless of theloading on the scale pan. By interconnecting the signals of the firstand second scale means so that the resultant output rellects thedill'erenee between these signals. vibration compensation at any loadingis achieved. in this mode of operation of the invention, compensationfor impact loading of the scale will also be achieved since such impactloading creates movements of the scale pan of greater than the velocityexperienced by normal teed rates so as to cause the second orcompensating scale means to respond. While the compensating system isreferred to herein as a second scale means it is recognized that thiscompensating system is not used [or weighing although its constructionis generally simiiar to a scale and it is used for measuring deflectionand force.

in another embodiment of the invention the coupling between the firstand second scale means is adjusted so that a response will be producedin the second or compensating scale means to substantially any weightchange in the first scale means scale pan, this response in thecompensating means being proportional to the feed rate on the scale pan.In this embodiment the signals from the first and second scale means arecoupled so that the re aultant is the sum of the two signals. As pointedout. hereinbetore in certain applications of the presently disclosedweighing system it is desirable to anticipate the material which is pastthe cut oil valve and in the air on the way to the scaie pan. Obviously,it the amount of material in the air is not taken into account, when thercade indicates cut oil and the cut of! valve is closed, such variationsin the additional material will cause variations in the weight of thepackages. By connecting the first and second scale means so that thecompensating means prodJccs a signal proportional to the rate of feed tothe first stale means and by adding the outputs, the resultant is avalue greater than the output of the first scale means and hen cut oiloccurs the material in the air will be taken into account. in thisembodiment the system, in effect, predicts the amount of material to beled on the basis of the rate at which material has been fed in theimmediately preceding instant.

An object of my invention is o provide a simple, rugged, compact,reliable balance system providing highly effective compensation forvibrations introduced on the pan or in the base structure.

Another object of my irivention is to provide means to compensate forimpact loading of articles forcibly striking the sale pan.

Still another obiect of my invention is to provide the above notedsuspensions with a rate sensitive intercoupling whereby a rateproportional signal is provided in the output of the secondary orcompensating suspension which will be proportional to material thatcontinues to be added to the scale alter the cut-o5 signal.

Another obiect of my invention is to permit either the sum or theelitism of the outputs of the scale means and compensating means to bemeasured as an output.

'Pat these and other obi-sets are refly derived from 3 the practice ofmy invention will be seen from subsequent detailed description whentaken together with the appended drawings, in which:

FIG. I shows a schematic diagram of the system showing both the scaleand compensating suspension and rate proportional intercoupling;

FIG. 2 shows a side elevation view 01 a preferred embodiment of myinvention showing a practical arrange ment of suspension elements,intercoupling dampers and recording transducers:

FIG. 3 shows an end view of the structure of FIG. 2 partially cut awayto reveal the scale pan damper and also providing an unobstructed viewof the auxiliary weight-deflected linear spring;

FIG. 4 shows a view taken along the section designated as 4-4 in FIG. 2;

FIG. 5 provides an example of suitable circuit connections for thedifl'erentialtranstormer displacement trany ducers:

FIGS. 6-9 show some actual records of signals derived from variousloading and vibration conditions on the preferred embodiment of FIG. 2.of which;

FIG. 6 shows the way in which vibrations of the base may be reduced inthe output signal;

FIG. 7 shows the compensation for the impact loading of hard articlesstriking the scale;

FIG. 8 shows schematically the problem involved in prior art devices incompensating for weight of material in the air;

FIG. 9 shows the way in which the present invention providescompensation for this eti'ect;

FIG. l shows an alternative balance structure wherein a pan balancesuspension replaces the spring suspension and a photoelectric transducerprovides means [or subtracting the relative displacements of scale andcompeneating suspensions; and

FIG. II shows a balance structure as in FIG. 10 but with a photoelectrictransducer which provides means for adding the relative displacement ofscale and compensat- Ing suspensions and a magnetic lntercoupling means.

Essential components of a system utilizing the teaching of my inventionare shown in FIG. I. Here a scale sus: pension designated generally byreference character 1 is mounted on a base 3 along with a somewhatcorresponding compensator suspension designated as 1. The scalesuspension is supported on a pillar member 4 which provides attachmentfor flcxure plates and 5b clamped apart at the other end by scale stem6. The resilient restoring force inherent in flexure pla es 5 may beaugmented by another spring. here shown as helical spring 13. In thisway, application of load in receptacle 8 placed atop pan 7 will cause alinearly proportional downward displacement of scale stem 6. Thesimilarly constituted compensator suspension 2 is attached to the base 3by means of pillar 9 serving to anchor one end of flexuro plates a and10b which are clamped apart at their other ends by stem 11. Stems 6 and11 are arranged to execute essentially parallel displacementsperpendicular to the base 3 and essentially parallel to columns 4 and 9.These suspensions would be independent except for the inter-couplingthrough dashpot 12 which provides a force proportional to the relativevelocity between stem 6 and stem ll. Displacements of the two stems thusintercoupled, may be measured inde pendently by displacement transducersT-l and shaft 6 and T-2 of shaft II. The outputs of these transducersmay be either added or subtracted depending upon the compensationdesired.

The situation where the dispaoement signals are to be subtracted isillustrated in FIG. 1. This connection would be desired it acompensation for the impact of a hard object was to be attained as wellas for cancelling the vibration signal; In general the vibrationsinherent in motor noise applied to the base will be of a relative highfrequency compared to the natural frequency of the suspensions. As such,the suspension will undergo motion relative to the base in phase withone another. The signals generated by their respective relativedisplacements would tend to cancel in the subtracted output of thedisplacement transducers.

It hard solid objects are dropped on the pan, the momentum of the impactis seen as imparting appreciable initial velocity to the pan 7. This maycause the displacement of scale stem 6 to over-shoot. However, with thepresent invention, the rate proportional coupling will produce acorresponding positive signal or displacement to the compensatingsuspension (e.g. of stem 11 in proportion to the downward velocity ofthe stem 6]. Sub traction ot the velocity proportion signal of stem IIwill tend to compensate for the over-shoot of stem 6, as willhereinafter be made clear. Vibrations on the pan 7, however, will betransmitted directly to the compensating suspension so that these likethe base vibrations will tend to cancel in the subtracted displacementtransducer signals. The dnshpot I2 may be adjusted so that movements atthe scale pan 7 caused by normal feed rates will not crrztte anysubstantial signal in the compensating system. In this mode oi operationcompensation will be provided for both vibration and impact loading.

There is alternately a second mode of operation in which thedisplacements of stems 6 and 11 would be connected so as to be additiverather than subtractive. Such positive corrective signal would beemployed if it were necessary to compensate the scale for the weight of"a powder or fluid still in the air and past the cutoff valve at the timethe given weight is indicated. Correct compensnlion is possible herebecause the more rapidly the receptacle is being filled, the greater therate of proportional displacement of the compensating suspension,corresponding to greater mass of material between the cutol! valve andthe receptacle. In this embodiment the dashpot is adjusted so that asubstantial signal is produced in the compensating system for normaliced rates, this signal being proportional to the rate at which materialis being fed to the scale means. Actual examples of the compensatingaction will be given later in connection with a practical embodiment ofmy invention.

In FIGS. 2. 3 and 4, a model of an operative form of the scale system inaccordance with the teaching of my invention is shown in detail. Herethe base 3 supports both the scale suspension 1 and the compensatingsuspension 2 from a single column 4 located at the right hand end of thefigure shown. In the preferred embodiment the post member 4 isrectangular in cross-section, being of substantial breadth so as to givesupport to rather wide tiexure plates 5a and 5b. The width of thesefiexure plates provides high lateral stillness ot the scale suspensionso that very little lateral displacement will result from correspondingforces applied to the pan 7. The lateral extremities of flexure plates5a and 5b are connected by double columns 62 and 6b serving to constrainthe flexure plates to parallel configuration and to space the endsequi-distant to the spacing imposed on post 4. In the configurationshown here, the flexure plates 5a and 5b lie on opposite sides of thebase plate 3 and accordingly must be interconnected by extending theposts 6a and 6b through the base in the holes provided therefor. Thedisplacement of stem 6 relative to the base 3 is indicated by the outputof displacement transducer T-I. Here a bracket 15 attached to stems 6provides mounting for a core member 16 oi the differential transformerwith body coils shown at 17. The body coils on the other hand aremounted to the base frame by means of brackets 18 and 19.

A fixed base support for the compensating suspension 2, corresponding topost 9 of FIG. I, is provided by boss members 9 fixed to column 4.Clamped by members 9, fiexure plates 10a and 10b are bifurcated so as tostraddle the necessary lateral extremities of posts 4 and 6. These areconnected at the outer movable extremity by double post members 1111 andttb attached to the single base plate 20. Vertical displacements of thebase are sensed by displacement transducer T-Z shown here as adifferential transformer having core member 21. a coil body 11 which issuspended from the base plate a by means of post 19 and bracket 18. Asin the case of the scale suspension, the compensating suspension alsoprovides no eellcnt lateral and longitudinal stiffness with highcompliance only in the vertical displacement direction.

'The coupling between suspensions 1 and 2 is provided by a dashpot showngenerally by reference character l2 and comprising a piston 15 immersedin a viscous fluid contained in cylinder 26 which in turn is attached tothe column 6 by means of the bracket 27.

in practical scales it also may be desirable to provide damping on thescale pan suspension itself. in H68. 2. 3 and 4 this is provided bydashpot 28 consisting essentially of piston 30, connected to the scalepan by means of stem 19, and a cylinder 3] attached to the base 3. Theviscous fluid contained in cylinder 31 is forced around the piston uponits excursions in and out of the fluid, thus providing a resistanceproportional to the time ra e of displacement of the piston relative tothe cylinder.

in the practical embodiment of the invention, the resilient llcxurcs 5and 10 are made from beat-treated beryllium copper, an alloy containingabout 2.5% beryllium has been found satisfactory. Other moving parts ofthe suspension can advantageously be constructed of a light structuralmetal, such as an alloy of aluminum, and the weight of the scale as awhole can be minimized by the construction of most of the essentialparts of such a light alloy. As to the damping flu d used in thedashpots, the liquid mcthylsiloxane has been found satisfactory in thepractical embodiment. in a typical case the compensator suspension wouldhave a natural frequency of one tenth of a second and the plungerdiameter and fluid viscosity of dasltpot 12 would be selected to producecritical damping of the compensator suspension when the scale positionis held clamped. As to the scale suspension itself the viscosity andplunger diameter of dashpot 28 would be chosen to provide criticaldamping, but here part of the damping would come from the compensatordas'npot which also provides resistance to scale movement through theinterconnection. it will be understood, of course. that variouscombinations of natural frequencies and damping constants can be used tofavor certain frequencies or certain compensation requirements. Theforegoing characteristics are cited only by way of illustration andshould not be construed to limit the scope of my invention to thespecific characteristics described by way of illustration.

it has been noted in the foregoing discussion that the verticaldisplacements of the scale and compensating members is detected bylinear differential transformers. These displacement transducers arequite conventional and do not require a detailed discussion here.Briefly, in each transformer primary windings and 36 are fixed in thecenter of the coil member and two secondary windings 37. 38, 39, and 40,respectively, are disposed symmetrically either side of it. When theprimary is encrgizcd and tltc cores and 46 are precisely centered withrespect to the two secondaries, equal voltages are induced in eachwinding. The two secondaries are connected in a bridge and the vc-Itageis cancelled. when a core is moved above or below this position, thesecondary voltages are unequal and '0 longer cancelled. This results inan output signal appearing across potentiometer 41 for the scale signal,or voltage divider 42 for the compensator, with phase mersing on eitherside of the null. The signals from eitbe: of the two sets ofdiflerentini transformers may be connected so as to add or subtractaccording to the compensation desired. In FIG. 5 the output at 44represents the difiexence or subtractive connection. when used in therate or additive connection for compensating for in the air, theresistance values in the voltage divider 42 can be fixed to provide theproper amount of rate signal for a given feeder or column height or thevoltage divider can be replaced with a potentiometer to permitadjustment of the amount of rate signal. The use of dili'erenllaltransformers as displacement transducers is by way of illustration of apractical embodiment of this invention. However, other types ofdisplacement transducers could be used without departing from the scopeof my invention.

For a more complete understanding of the operation of my improvedweighing device, it is helpful to consider its mechanics as a system ofcoupled, damped, harmonic oscillators. The natural frequency of thescale suspension is determined from design considerations including theload to be carried and the deflection desired for maximum accuracy andsensitivity. Whatever this frequency must be, however, the compensatorsuspension is usually designed to have a natural frequency substantiallyhigher than the natural frequency of the scale suspension. Usually thisis higher by factor two. This is done to provide stiller couplingbetween the two suspensions and to reduce the settling time. For acompensator suspension of given mass, the dashpot resistance needed forcritical damping is reater if the natural frequency is higher. Thisimproves tracking between the two suspensions under conditions of panvibration and impulsive loading. it also shortens the recovery orsettling time because less time is needed for the compensator to reachits equilibrium condition if its natural frequency is higher. Unlike thescale suspension, however, the compensator need early no load, or objectbeing weighed, so it may be much lighter susension. In view of its lowermass its coupling to the scale suspension tends to have very littleeffect on the natural characteristics of the scale suspension.Accordingly, the force applied to the compensating suspension may beconsidered as simply proportional to the velocity of the primary orweighing scale suspension.

Just how effective this type of compensation can be is illustrated bythe actual records made with a practical model of my inventionillustrated in FIGS. 6 through 9. In FIG. 6 the vibration is introducedthrough the base by means of a motor attached thereto with an eccentricon its shaft. The drawing shows graphically the deflection of the scaleand the compensator both reflecting the vibration. Since these signalsare connected to subtract to reduce each other, the resultant trace isevidence of the degree of cancellation of the vibration signals.

The curves of FIG. 7 show the effect of impact of a hard object on thescale pan or impulsive loading. This condition will be encountered whenhard candy, cookies, otato chips. caramels, etc. are being weighed anddropped from some distance. In this particular instance, a 5 gram weightwas dropped on the scale shown in FIGS. 2-4 front a distance of aboutltd inches. The scale trace shows the signal from the scale suspensiontransducer, which would normally be obtained without compensation. Theovershoot due to impact is about 13 millimctcrs. When the compensatorsignal is combined with the scale signal the resultant is an overshootof about 4 millimeters. This compensation could be further increased byincreasing the frictional coupling in the cottpling dashpot, so as toreduce the overshoot to zero. It should be noted that it requires onlyabout a fifth of a second for the scale to reach its equilibriumposition after the impulsive loading. Where no compensation is provided,but damping made sufficient to avoid overshoot, the time required toreach equilibrium would naturally be much greater than this, as it is atime only the order of the period of the primary or weighing suspension.This compensation system thus permits a substantial in crease in theweighing speed of my scale.

It is important to note here that my invention permits an alternativemode can be made for variations of the weight of powder or of operationin which compensation liquid in the air at the time the filling valve isclosed. The errors which normally result in the conventional scale withchange in load and filling rate are seen in FIG. 8, where the upperfigure shows that at a slow rate of load ing the final weight varieslittle in excess of the cut off level obtained. However, in rapidfilling on the same scale, the weight of material in the air at thetinieof cut off will naturally be much greater so that the final weightwill be considerably in excess of the cut oil level, or the levelobtained when the filling rate is slow, as represented by the lowertrace.

To employ my invention to properly compensate for the weight of thecolumn in the air, the displacement signals from the differentialtransformers T-l and T4 are arranged to be additive rather thansubtractive. The rate of filling will be assumed relatively slowcompared to the natural frequeneyof either suspension so that thecompensator velocity proportional signal is simply proportional to therate of filling. The rate of change of weight is proportional to theweight of material in the air, therefore, the signal from thecompensator could he considered to be weighing the material in the airor be proportional to this amount. Because the two voltages areconnected to add. the compensating signal causes the resulting signal toreach the cut of! value signal sooner at higher rates of feed, as shownin solid line in FIG. 9. Thus the filling or cut-o5 valve is actuated,t.e., cut ofl, when the resulting signal reaches the predetermined cutvalue or trip level. The dashed line portion 0] FIG. I illustrates Inblock form the remaining elements of the overall system for theoperational mode described above, the combined outputs of thetransformer: T-I and T-Z being shown as being connected to a blocklabeled Cut 017 Valve And Actuator which is Indicated to control thematerial supply, the cut valve, a: stated, being octuated when thecombined rate and load signal reaches the trip level. The dash lines onthe curve show the reduced compensation effected and required at thelower feed rates.

The effects of the damping applied in the preferred embodiment throughdashpot 28 on the response of the primary or scale system will beevident from an inspection of FIG. 7. It should be noted in additionthat this damping is desirable because it prevents the excessiveexcursions of the primary weighing system during oscillation. Theseoscillations could be great enough to exceed the linear range of thedifferential transformers and thus adversely affect the accuracy of thescale indication. The damping also tends to reduce oscillations inducedwhen adding weights suddenly or those induced by vibrations. This isusually helpful because there can be small relative motion between thetwo members during oscillation which causes imperfect cancellations.

The foregoing description has been purposely specific to a preferredembodiment of my invention. particularly to dashpot coupled springsuspensions. However. with this specific example by way of illustration,it will be appreciated that by basic concept and teaching is of generalapplicability to the art of automatic weight sensing. In general, it isa basic teaching of my invention that it is possible to anticipate thematerial that will continue to be added to the scale after the cut offsignal by detecting the rate of change of weight; that this rate sensingcan be done in a very simple manner by coupling one force sensitivesystem to another by a dash ot; that the force sensitive systems neednot be limited to spring suspensions but may include the gravityactuated beam balance as well as the beam balance with stiffnessaugmented by resilient members. Likewise various displacement dctectingsystems may be employed, such as photoelectric transducers.Alternatively, other types of rate proportional intercoupling may alsobe employed.

For particular examples of such systems, consider the beam balance shownin FiG. where pan stems 50 and 51 are suspended on opposite sides ofsupporting post lll 5?. by arms 53 and 54. Restoring force can be builtinto the system by placing the fulcrums 55 and 56 in the fixed post 52 apredetermined distance above a line connecting stem fulcrums 57 and 58or 59 and 60, respectivcly. This may be augmented or substituted byspring members 61 and 62 connected between base 63 and opposite region:of lower cross arm 54. The selection of spring compliance will permitconvenient adjustment of the sensitivity and natural frequency of theprimary balance su'r ension.

The secondary or compensating suspension is likewise a beam suspension,wherein stem member 64 is attached to post 52 by parallel connectingarms 65 and 66. A counterweight 68 provides gravitational neutrality andspring 67 augments whatever gravitational restoring force may beinherent in this suspension as required for a proper frequencyrelationship between primary and compensating suspensions. The velocitysensitive coupling between suspensions is provided here by fluid dashpot68. The primary suspension is damped by dashpot 69 connectcd between theprimary suspension and the base 63. With the foregoing description. itshould be apparent to one skilled in this art that the dynamic responseof this system may be made quite equivalent to that for the liexureplate suspensions previously described.

For the measurement of the displacement responses of primary andsecondary suspensions, a novel photm electric-optical system is shown inconnection with the balance structure. In FIG. 10 it is arranged tosubtract the relative displacements, and thus to compensate for impactand vibration. Here a light source 70 and condensing lens 71 tilts theaperture of lens 72. A shutter 73 connected to stem 50 is focused atscreen 74 by lens 72. if unobstructed the light from lens 72 proiectsupon photocell 75. A fixed maslt 74 prevents light below the opticalaxis of the system from falling upon the photocell 75. Thus, in theneutral position no light is transmitlcd to detecting photocell 75.Downward motion of shutter 73 causes upward movement of the image abovemask 74 allowing light to strike the photocell. Downward motion of lens72 causes downward motion of tlze image. Therefore, substantially equalmovements of primary and compensating suspensions will cause oppositemovements of the image relative to mask 74, thereby causing cancellationin a manner similar to that shown in the flexure suspension embodiment.

The structure, for the sake of simplification, shows a means ofobtaining a large change in the photo-electric cell output signa! when agiven weight level is reached. This could be used to cut off a feederwhen a desired weight indication is reached. Two or more photocells andmasks could be used if additional weight levels were to be sensed. it isalso possible to achieve a signal level proportional to weight by theuse of V-shaped mask or shutters as is well known in the art.

FIG. 11 shows a balance structure similar to that of FIG. 10 except thata magnetic type velocity sensitive coupling 76 reglaces the dashpot (-8.Of particular note is the photoelectric displacement sensor which hasbeen deviqcd to add displacements, thcrc-y providing an anticipatorysignal proportional to the velocity of the primary suspension. Anadditional stationary lens 77 is added for the purpose of inverting theimage or shutter 73. A mask 78 has accordingly been provided on theupper side of the optical axis. Downward motion of stem 50 causes theimage at 78 to move downward. Downward motion of lens 72 also moves theimage downward, allowing more light to reach the photocell. As thedisplacement of lens 72 is proportional to the velocity of the primarysuspension and stem 50 and as the move ment of either suspension causesa shift in the image in the same direction, the two motions are additiveand thtdesired anticipatory compensation results.

The magnetic coupling 76 which here replaces the fluid coupling ofpreviously described embodiments, consists BEST AVAILABLE SOPY:ssentially ot a magnet 79 attached to stem 50 and an llutninum vane 80attached to stem 64 so as to pass be- Ween the poles of the magnet.Relative motion of the nagnet sets up eddy currents in the vane, theenergetics at which result in a force proportional to the relativevelocity.

What i claim is:

[1. A weighing system comprising a weighing pan, means responsive to aload applied to said pan for producing a first signal proportional tothe applied load, and means coupled to said first named means forproducing a second signal proportional to the rate of change of saidfirst signaL] [2. A weighing system for weighing increasing applied loadand for anticipating future load comprising means for weighing theinstantaneous applied load and for producing a measured applied loadsignal, means for determining the rate at which the load is beingincreased and for producing an incremental rate signal, and means forpredicting the future load based on the rate at which the previouslyapplied load is increasing by adding the incremental rate signal to themeasured applied load signal] 3. A weighing system comprising a firstscale. first transducer means for transmitting a signal proportional tothe load applied to said scale, a compensator including a suspensioncoupled to said scale, second transducer means [for transmitting asignal proportional to the movement of said compensator], rate sensitivemeans for producing a second signal proportional to the rate of movementof the scale for connecting said scale and compensator whereby saidsecond transducer means produces said [a] signal proportional to therate of movement of said scale and means connecting said first andsecond signals.

4. A weighing system for weighing applied load and for compensating forexternal vibration and impact loading comprising means for weighing theapplied load on a scale to produce a first signal having components ofload and vibration, a compensator coupling the scale to the compensator,means to transmit movement to the compensator in response to vibrationof the scale and instantaneously applied impact load causing movement ofthe scale to produce a second signal from the compensator withcomponents of vibration and impact loading of said scale and meanscoupling the first and second signals to reduce the extraneous efi'ectsof the determination of the weight of the applied load caused byvibration and impact load.

5. A weighing system for weighing normally applied loads and forcompensating for impact loading and external vibration comprising aweighing pan, first means operativcly connected with said pan forproducing a first signal proportional to the applied load and toexternal vibration, second means for producing a second signalproportional to the rate of change of applied load and means couplingsaid first and second means, said coupling means transmitting a signalfrom the first means to said second means proportional to the rate ofchange of said first signal whereby said second means produces a signalof vibration and impact loading of the weighing pan, and meansconnecting said first and second signals to reduce he extraneous effectson the determination of the weight of the applied load caused byvibration and impact load- 6. A balance comprising (a) a base memberproviding a reference frame for the structure,

(b) a primarysuspension attached to said base,

(c) a. primary displacement element constrained by said primarysuspension to essentially rectilinear displacetrients proportional to anapplied load,

() a seconda y suspension attached to said base,

(e) a secondary displacement element constrained by said seconds,suspension to essentially rectilinear 10 rcction essentially parallelthe displacement direction of said primary element,

(l) a velocity sensitive force transmitting element coupling saidprimary displacement element to said secondary displacement clement soas to compensate for the efiects of impact and vibration loading, and

(g) means opcratively associated with said primary and secondarydisplacement elements [or measuring the displacements of said elements.

7. A balance as in claim 6 [but] and including a dash pot coupling saidprimary dispiacnncnt elements to said base.

8. A balance as in claim 6 [but] and in which the natural frequency ofundampcd oscillation of said secondary suspension is substantiallyditl'crent from that of said primary suspension.

9. A balance as in claim 6 [but] and in which the natural [requcncy ofundamped oscillation of said secondary suspension is approximately twicethat ol said primary suspension.

10. A balance as in claim 6 [but] and in which said primaryvelocity-sensitive force-transmitting element provides approximatelycritical damping of said secondary suspension when said primarydisplacement element is held fixed with respect to said base.

ll. A weighing apparatus [system for compensating weight indicia [orcfl'ects of impact and vibration] comprising (a) a primary weighingsystem having an element deticctable in direct proportion to appliedload,

(b) a secondary weighing system having an element dellectable in directproportion to applied load,

(c) a velocity-sensitive force-coupling connected be tween said primaryand said secondary dcliectable elements so as to compensate for the(fleets o] impact and vibration loading, and

(d) means to measure the dilierence ol' the deflections of said primaryand said secondary defiectabic ele ments.

12. A system as in claim 11 but wherein said deflcolion measuring meansincludes (a) a primary mask mounted on said primary deflectable clement.

(b) means for illuminating said mask,

(c) a lens mounted on said secondary deflectable ment focusing an imageof said mask,

(d) a fixed photoelectric detector receptive of the illuminated image ofsaid mask, and

(e) a secondary mask mounted so as to intercept the image of saidprimary mask whereby light is trans niitted to the photocell when thedeflection of said primary mask exceeds a fixed level less an amount proortional to the deflection of said secondary dc ficctablc element.

'3. A system for compensating weight indicia for material still inprocess of entry at the time a cut-off threshold is reached comprising(a) a primary weighing system having an element deflectable in directproportion to applied load,

(b) a secondary weighing system having an element dcllcctable in directproportion to applied load,

(c) a velocity-sensitive, force-coupling connected between said primaryand said -econdary deflectable elements so as to compensate [or materialstill in the process of entry at the time o cut-ofi threshold Ltreached, and

(d) means to measure the sum of the deflection of said primary and saidsecondary detiectable elements.

14. A system as in claim 13 [but] and wherein said deflection measuringmeans includes (a) a primary mar; mounted on said primary delicctzblcelement,

(b) means for illuminating said mask,

(c) a fined lens focusing an image of said mask,

(d) a lens mounted on said secondary deflectable eleele- (e) a tiredphotoelectric detector receptive of the illuminatcd image of said mask,and

(l) a secondary mask mounted so as to intercept the image of saidprimary mask whereby l eht is transmitted to the photocell when thedeflection of said primary mask exceeds a fixed level plus an amountproportional to the dcllectionot said secondary deflcctable element.

15. A system as in claim 13 but wherein said velocityscnsitive,force-coupling consists of a magnet mounted on one dcllcctable elementand a conductive vane mounted on the other deficctable element so as topass between the poles of the magnet upon relati e dcllcction of the twoelements.

16. A weighing system comprising, in combination, a base. aprimarysuspension including at least one resilient llcrture plateattached to the base, first means [or measuring deflection of saidprimary suspension, a secondary suspension including at least onefiexure late attached to the base, second means [or measuring deflectionoi said secondary suspension, a [rate] velocity sensitive couplinginterconnecting said primary and secondary suspensions at to compensatefor the eflect: of impact and vibration landing, said [rate] velocitysensitive coupling comprising a dashpot having a cylinder and iston, thepiston being coupled to one of said suspensions and the cylinder beingcoupled to the other 0t said suspensions, and means connecting saidfirst and said second measuring means. 4

11. A weighing system comprising, in combination, a supporting frame, afirst scale including fiexure plates attachcd to said frame. a secondscale including flexurc plates attached to said frame, a [rate] velocitysensitive coupling interconnecting said first and second scales [ofcompensating for the eflects of impact and vibration loading, said[rate] velocity sensitive coupling including a dsshpol having a pistonand fluid filled cylinder, the cylinder being coupled to one of saidscales and the piston being coupled to the other of said scales andmeans for measuring the difference in deflection of said first andsecond scales.

X8. A weighing system comprising 1 supporting frame, a first pair offlcxure plates having one end secured to said supporting frame, a scalepan supported by the other end of said flcxure plates, a second pair offlcxure plates having one end secured to said supporting frame, a ratesensitive coupling interconnecting the other end of said second pair offlexute plates with said first pair of ilexure plates and electricalmeans (or measuring the deflection of said first and second pair offlexure plates and for producing an output signal directly proportionalto the ap plied load on said scale pan and reducing the extraneouscll'cets on the determination of weight caused by vibration and impactload.

19. A weighing system according to claim 18 wherein said electricalmeans includes a linear diflerential transformer.

20. A weighing system comprising. a base, a primary suspension systemincluding a pair 0! flexurc plates having one end secured to said base,a weighing pan sup orted by the other end of said tlcxurc plates, 1 dashot connected between the primary SIL'PCUSiOD system and the base, asecondary suspension system. said secondary suspension system includinga pair of flexure lates having one end thereof secured to the base, theother end of the second pair of flexure plates being interconnected, arate sensitive coupling including a piston and tiuid filled cylinderinterconnecting the primary and secondary suspension systems, the pistonbeing connected to that end of one pair of flexun: plates remote fromthe base and the cylinder being connected to the end of the other pairof ficzure plates remote from the base, first transducer means forproducing and transmitting a sigma proportional to the load applied tothe weighing pa; tssd vibration and r Mar in-'7. rec-3nd transducertrio-: 2: for pzooucizg and transmitting a signal proportional to themovement of thesccondary suspension system due to vibration and impactloading and electrical circuit means interconnectin; said first andsecond transducer means whereby the signal from said second transducermeans is substractcd from the signnlfrom the first transducer means sothat the output signal is proportional to the actual load splied to theweighing pan so as to reduce extraneous etlccts caused by vibration andimpact loading.

21. A weighing system according to claim 20 and further including afirst dashpot connected betv'tecn the primary suspension system and thebase and a second dashpot connected between the secondary suspensionsystem and the base.

[22. A weighing system comprisingls scale, a compcnsnlor, velocitysensitive force transmitting means coupling said scale to saidcompensator, and means for determining the relative displacement betweensaid scale snd said compensntcn] 23. A weighing system comprising ascale, a cum pcnsaror [or compensating for the eflect: of impact andvibration loading, velocity :enrirlve force trammlttlng mean: couplingsaid seal: to said compensator, and mean:

. for determining the displacement between said scale and midcompensator so its to compensate for the efiects of impact and vibrationloading.

24. A weigltlng system [or welgltlng lncrrnrlng applied load in amaterial filling process comprising a scale, a compensator forcompensating for the material that wlll continue to be added to thescale alter a cut 05 signal to the material filling process, velocitysensitive {once trans milling mean: coupling raid :cnle to raidcompentator, and means for determining the displacement of said xnle andsaid compensator so a: to compensate for the materlnl that will continueto be added after said cm 05 signal to the filling process based on therate at which the previonsly a plied load is increasing.

25. A weighing system for weighing increasing applied le d in a materialfilling process wherein material is fed from a product supply to a scaleand for obtalnlng a predetermined final load weight, comprising meansfor weigh lttg the instantaneous applied load and [or produclng ameasured applied load signal, mean: for detemtlnlng the rate at whichthe load I: being increased and {or produc lng a rare signal, means [oradjusting the rate signal to be substantially representative of theweight 0/ the material that will continuero be added to the scale aftera cut 05 signal to the filling process l: produced, mean: [of combiningthe adjusted rate signal and the measured up plied load signal, andmean: for produclng raid cut 05 signal {or culling 06 the fillingprocess when the weight reprcrcnrerl by the combined signal: issubstantially equal to the predetermined final load weight so as tocompensate for the weight of the material that will be added to thescale alter the cut 05 signal cut: 05 the filling process and therebyobtain raid predetermined final load welgltL.

26. A weighing system for weighing Increasing applled load in a materialfilling process wherein material is led from a product .ruppl y to ascale and for producing a predetermined final load weight, comprisingmeans for welglting the instantaneous applied load and [or producing ameasured applied load signal, mean: [or determining the rate at whichthe load is being lrtcrcared and {or produc' lrrg a rate .n'gnal, andmeans {or adding the rule signal to the measured applied load signal toproduce a cut 017 .n'g no! for cutting 05 the filling process whichcompensate: for the material that will continue to be added to the scaleafter the cut 0H signal to the filling procet: based on the rate atwhich the previously applied load is increasing thereby producing .rat'dpredetemtlned final load weight.

27. A system or claimed In claim 26 wherein cut 05 it provided by a cut05 valve when the cut 05 signal reaches a predetermined va uecorresponding to said predetermine-d final load weight and the Materialis weighed in a EST AVAILABLE COP,

acute pan and Lt gravity fed to the x01: pan at a substam daily constantrate.

28. A system as clalmcd in claim 27 wherein said ratcdetemlt'nt'ng meanscomprise: a mechanical dashpot.

29. A system as claimed in claim 27 whtret'n .rat'd ratedetamlnlng meanscomprises a mechanical dashpot.

References Cited The fo1lowing rcfcrcnccs, citcd by the. Examiner, are

patcnL UNITED STATES PATENTS 2,767,975 10/1956 Horst ct. a1. 177-2002,793,026 3/1957 Giardino et a1. 177-185 14 Gregory 177-122 Appius177-229 Sher et a1. 177-229 X Knobcl 177-210 X Thomson 177-210 lungmaycr177-210 X Giulia 177-229 X Koch et a1. 177-210 of record in the patentedfile of this patent or the original 1.; RICHARD WIUGNSON' Primary EnminV. W. MISKA, Assistant Examincr 11.5. C1. XJL

